How do dolphins see in murky water?

Who turned the lights out?  Humans use their eyes to see, and of course dolphins have eyes too (though some types of river dolphin are almost blind). Dolphins probably only see in black and white and one eye can look forward, while the other looks back.

 

Turn the lights out and humans are left to fumble around in the darkness. Dolphins have another sense they can rely on, called 'echolocation'.

 

Echolocation is a bit like the sonar, or pulses of sound, that submarines use to find their way, or bats use when flying at night.

 

Sound travels better in water, and up to four times faster than it does in thin air and dolphins can hear a much wider frequency of sounds than humans can.

 

Dolphins use air sacs under their blowhole to generate a rapid series clicks which can, amazingly, be up to 2000 clicks per second. When the clicking sound bounces off something else in the water, the echo is detected by the dolphin’s ‘melon’ which is a fatty ball of tissue at the front of the head, in front of the dolphin’s eyes. The melon focuses the sound like a lens. The sound reverberates through tissue in the lower jaw and is passed on to the inner ear (dolphins of course don’t have sticky-out ears like we do).

 

Some clicks are low intensity, and sound a bit like a creaking door. Higher frequency clicks sound like a high-pitched buzz and paint a more detailed picture in the dolphin’s brain of what is around them. 

 

In one experiment, a dolphin could use sonar to tell if something was made of metal, wood or plastic from 100 feet away. It seems that dolphins echolocation is much more subtle and sophisticated than anything similar that humans can create using technology.

 

Doctor dolphin? Sound even penetrates living bodies, so in a way, dolphins can see through each other’s bodies. This may explain reports of dolphins taking a particular interest in pregnant women or people with surgical steel implants, as they can detect what our humans eyes cannot. Echolocation may also help dolphins figure out how other dolphins are feeling.

 

What’s for dinner? Dolphins use their echolocation for finding food, such as fish swimming in the water. They’ve also been observed using it in the Bahamas to find fish buried in the sand at the bottom using a technique called 'crater fishing'. 

 

Dolphins may use their echolocation to stun fish. Dolphins have been reported to emit sounds of over 200 decibels, when an air-raid siren would be about 150 decibels. Presumably a disorientated fish cannot swim away, and can be more easily caught.

 

Source: White page 26